Search

Liquid level measurement in microfluidics is challenging, where a sensor with ultra-high sensitivity but miniature in nature is demanded. In this paper, we propose for the first time a microsized fiber sensor structure in both diameter and length for microfluidics applications, which is capable of sub-micrometer scale liquid level measurement. The sensor is simply fabricated by fusion splicing a short section of a hollow core fiber (HCF) between two singlemode fibers (SMFs). HCFs with different air core diameters (10 µm, 20 µm, 30 µm) were investigated and it is found that for a given length of HCF stronger resonant dips were excited in transmission for the HCF with a smaller air core diameter. Thus the HCF structure with an air core diameter of 10 µm (HCF-10) was used for demonstration of high sensitivity liquid level measurement in microfluidics. Simultaneous excitation of both Anti-Resonant Reflecting Optical Waveguide (ARROW) guiding mechanism and Mach-Zehnder interferometer (MZI) in transmission is demonstrated in such an HCF-10 structure when HCF-10 is longer than the critical length. A maximum sensitivity of 0.042 dB/µm (corresponding to a calculated liquid level resolution of ~0.23 µm) was experimentally achieved with an HCF-10 length of ~867 µm, which is three times higher than that of the previous reported to date of the most sensitive fiber optic liquid level sensors based on intensity modulation. In addition, the proposed sensor shows good repeatability of measurement and a very low cross sensitivity to changes in the surrounding refractive index.

Long-range surface plasmon resonance (LRSPR), generated from a coupled plasmon polariton in a thin metal slab sandwiched by two dielectrics, has attracted more and more attention due to its merits, such as longer propagation and deeper penetration than conventional single-interface surface plasmon resonance. Many useful applications related to light–medium interaction have been demonstrated based on the LRSPR effect, especially in the sensing area. Here, we propose and demonstrate an LRSPR-based refractive index sensor by using a SiO2-Au-TiO2 heterostructure, in which a D-shaped honeycomb-microstructure optical fiber (MOF) is designed as the silica substrate and then deposited with a gold film and thin-layer titanium dioxide (TiO2). By using the full-vector finite-element method (FEM), this heterostructure is numerically investigated and demonstrated to excite LRSPR without a buffer layer, which is usually necessary in previous LRSPR devices. Through comprehensive discussion about the influence of structural parameters on the resonant wavelength, the excitation of the LRSPR in the proposed heterostructure is revealed to be highly related to the effective refractive index of MOF’s fundamental core mode, which is mainly determined by the MOF’s pitch, the thicknesses of the silica web and the planar-layer silica. Moreover, the thin-layer TiO2 plays an important role in significantly enhancing the resonance and the sensitivity to analyte’s refractive index as well, when it is coated on the top of the Au film rather than between the metal and waveguide. Finally, the proposed LRSPR sensor based on SiO2-Au-TiO2 heterostructure shows an ultra-high wavelength sensitivity of 20,100 nm/RIU and the corresponding minimum resolution is as low as 4.98×10−7 RIU. Thus, the proposed LRSPR device offers considerable potential for sensing applications in biomedical and biochemical areas.

A cascaded fiber sensor for measuring different curvature ranges based on the cladding mode resonance in double-cladding fiber is proposed. It is formed by double-cladding fiber and single-mode fiber. Based on the evanescent wave coupling principle, the cladding mode resonance phenomenon in double-cladding fiber is illustrated. The transmission spectrum with different length are also analyzed. The experimental results show that the resonance wavelength changes with the length of double-cladding fiber. When the fiber length is 22 mm, the transmission spectrum is blue-shifted as the curvature increases in minor range of 0–0.204 m−1, the corresponding curvature sensitivity can be up to −19376.48 pm/m−1. When the fiber length is 20 mm, the corresponding curvature sensitivity can be up to −4161.73 pm/m−1 as the curvature increases in large range of 0–1.06 m−1. The proposed curvature sensor has the characteristics of simple structure and high sensitivity, so it has a good application prospects in large bridges, industrial buildings and other curvature measurement situations.

We report the use of a femtosecond infrared (fs-IR) laser to produce random grating structures in optical fibers for fiber sensor and fiber laser applications. The plane-by-plane method of inscribing various gratings is presented. We review our experimental results over the past 5 years of the applications of fiber random gratings for distributed temperature measurements, fiber lasers and fiber laser sensors. The potential applications of fs-IR laser processed optical fibers in structure health monitoring, harsh environment sensing, perimeter intrusion detection and encrypted communication will be discussed., Fiber Optic Sensors and Applications XVII, April 12-17, 2021, Online Only, United States, Series: Proceedings of SPIE

Distributed fiber optical systems (DFOS) allow deployed optical cables to monitor the ambient environment over wide geographic area. We review recent field trial results, and show how DFOS can be made compatible with passive optical networks (PONs).

We demonstrate fiber optic sensing systems in a distributed fiber sensor network built on existing telecom infrastructure to detect temperature, acoustic effects, vehicle traffic, etc. Measurements are also demonstrated with different network topologies and simultaneously sensing four fiber routes with one system.

There is an optical interference noise in the conventional Raman-based fiber-optics distributed sensing, which results in a poor temperature resolution performance. In addition, the traditional whole-fiber demodulation principle complicates the operation steps of the system. In this paper, a novel dynamic difference attenuation recognition (DDAR) principle is operated in the DDP scheme (dual demodulation principle) and the SDP scheme (self-demodulation principle) respectively. It not only helps to eliminate the optical interference noise, but also omits the whole-fiber calibration process. In this experiment, a temperature resolution of 0.30 &deg, C (17.0 km) is achieved through using the DDP scheme based on the DDAR principle, and the measurement time can be shortened to 1.5 s. Meanwhile, a temperature resolution of 0.18 &deg, C (17.0 km) is obtained for the SDP scheme under the DDAR principle. The SNR of DDP and DSP schemes can be optimized to 12.82 dB and 13.32 dB by the proposed DDAR technology. Furthermore, the temperature resolution performance under a large temperature measurement range (0&ndash, 1000 &deg, C) is theoretically analyzed. The results indicate that the temperature responsivity for DDP and SDP schemes are parabolic and linear type respectively, which causes the temperature resolution of the two schemes to show a different trend with the change of temperature. The proposed DDAR method also can improve the temperature resolution in such a large temperature measurement range.

A temperature sensor was fabricated with a functional conductive poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) coating on a long-period fiber grating (LPFG). The LPFG was fabricated by laser-assisted wet-chemical etching for controlling the grating depth of the LPFG after the treated surface of an optical fiber was inscribed by laser light. The functional conductive polymer acts as a temperature sustained sensing layer and enhances the grating depth of the LPFG sensor as a strain buffer at various temperatures. The sensor was subjected to three cycles of temperature measurement to investigate the sensor&rsquo, s wavelength shift and energy loss when exposed to temperatures between 30 and 100 &deg, C. Results showed that the sensor&rsquo, s average wavelength sensitivity and its linearity were 0.052 nm/&deg, C and 99%, respectively, average transmission sensitivity and linearity were 0.048 (dB/&deg, C) and 95%, respectively.

Intensity-Modulated optical fiber sensors are popular because of their simple construction and inexpensiveness. The major problem while the development of an intensity-modulated fiber sensor is to have a test bench that can test such sensors with different light sources. The stability of the intensity of LED sources is a major challenge. The paper describes the microcontroller-based test bench which takes care of the intensity stability of the light source. This test bench also takes care of stray radiations. The standardization of the optical fiber sensor is a big challenge and this effort is a small step towards it.

In this paper, an all fiber optic sensor based on a Mach-Zehnder interferometer (MZI) has been proposed for the simultaneous measurement of underwater pressure and temperature, utilizing a dual-mode fiber (DMF) which has been specially designed, and supporting only the LP01 and LP02 modes propagating in the fiber. In this design, an in-line MZI sensor that was constructed by splicing a DMF between two pieces of single mode fibers, shows a critical wavelength (CWL) which exists in the transmission spectrum of the LP01-LP02 mode interference. Since the two peaks, located closest to the CWL (and from both lower and higher wavelengths), shift in opposite directions and show different sensitivities under temperature and water pressure variations, the DMF-MZI sensor is capable of measuring both the water pressure and the temperature simultaneously. The CWL-based interference spectrum is stable with the variation of underwater salinity or impurities seen around the fiber surface and independent of the polarization states of the transmission light. As a result, in the operation of the DMF-MZI sensor, underwater pressure and temperature sensitivities increase significantly, when the peak wavelengths are close to that of the CWL. A theoretical analysis has been developed and used to predict that the sensitivities of this specific DMF-MZI structure which can be further improved by increasing the physical length of the DMF and by adjusting the position of the first left/right peak to be closer to the critical wavelength. This co-located, multi-parameter all-fiber sensor developed in this way and showing relatively high sensitivity is easy to implement in the underwater environment. It does not require a complex shell design and the peaks nearest to a CWL are convenient, allowing easy identification and detection, thereby providing a large measurement range to satisfy the requirements of practical marine and fresh water measurements.

In this paper, a new sensor system for simultaneous and independent multipoint strain and temperature measurements is presented. The interrogation of the sensing heads has been carried out by monitoring their FFT phase variations. In particular, two of each microstructured optical fiber (M0F) cavity interference frequencies were used for the measures. This method is independent of the signal amplitude and also avoids the necessity of tracking the wavelength evolution in the spectrum, which can be a handicap when there are multiple interference frequency components with different sensitivities. The sensing heads present birefringent and multimodal properties and therefore both characteristics lead to their own interference with different properties and sensitivities. The multiplexing capability of the sensing heads and the interrogator method has also been tested and validated. Sensors were operated within a range of temperature 30°C-80°C and a deformation of ̴450 με was applied. Crosstalk between measurements can be corrected through simple math operations leading to independent and crosstalk-free multipoint and multiparameter sensors. This work was supported in part by the Spanish Comisi´on Interministerial de Ciencia y Tecnolog´ıa within projects TEC2016-76021-C2-1-R and TEC2013-47264-C2-2-R, in part by Cost action MP1401, and in part by FEDER funds from the European Union.

The effect of &gamma, ray irradiation on the surface plasmon resonance (SPR) sensing capability of refractive index (n = 1.418&ndash, 1.448) of the silica glass optical fiber comprised of germano-silicate glass cladding embedded with Au nano-particles (NPs) was investigated. As the &gamma, ray irradiation increased from 1 h to 3 h with the dose rate of 1190 Gy/h, the morphology of the Au NPs and the SPR spectrum were found to change. The average diameter of Au NPs increased with the aspect ratio from 1 to 2, and the nano-particles became grown to the clusters. The SPR band wavelength shifted towards a longer wavelength with the increase of total dose of &gamma, ray irradiation regardless of the corresponding refractive indices. The SPR sensitivities (wavelength/refractive index unit, nm/RIU) also increased from 407 nm/RIU to 3553 nm/RIU, 1483 nm/RIU, and 2335 nm/RIU after the &gamma, ray irradiation at a total dose of 1190 Gy, 2380 Gy, and 3570 Gy, respectively.

Fiber optic sensor with an SC source through at 1km optical fiber to obtain a broad spectrum in the 1300-1650 nm section for the realization of a displacement sensor by means of a Fabry-Perot interferometer.

We developed and optimized a new fiber optic sensor using palladium foils attached to optical fiber Bragg gratings (FBG) for hydrogen measurements. Fifteen in parallel processed sensors were characterized and qualified in two custom tailored experimental set ups and their response to a 5% hydrogen/nitrogen gas mixture and the same gas bubbled trough transformer oil was measured. The hydrogen response is similar for both medium and close to the theoretical maximum sensitivity, but the response time was found to be very different, much slower in oil than in gas. A theoretical comparison of hydrogen diffusion trough palladium and hydrogen absorption on the palladium surface as well as a measurement of the hydrogen uptake and diffusion trough the oil to the sensor have been done to investigate the origin of the different response time. They indicate that the response time determining step is the absorption of hydrogen on the palladium surface and that this process is slowed down in oil compared to a pure gas environment.

Brillouin scattering properties of silica fibers at 850-nm wavelength were experimentally investigated using a Brillouin optical time-domain analysis scheme. In the single-mode 780-HP fiber, the Brillouin frequency shift (BFS) and full width at-half maximum of the Brillouin gain spectrum were found to be ~19795 and 90 MHz, respectively. The estimated peak Brillouin gain is 0.32 (mW) -1 . The temperature and strain dependences of BFS were determined as well. Distributed sensing capability was demonstrated at a minimum spatial resolution of 1.5 m and a fiber length of 100 m. As a proof-of-principle, the temperature and strain dependences of the BFS in SFM-28 fiber have been determined at 850- and 1550-nm wavelengths, suggesting its possible use for temperature/strain discrimination.

We report distributed temperature measurements based on Raman scattering performed during steady state $\gamma $ -ray irradiation at a dose rate of 1 kGy( ${\rm SiO}_{2}$ )/h and up to a total ionizing dose (TID) of $\sim 0.1\ \hbox{MGy}$ . We characterize on-line the evolution of the performances of a single-ended Raman distributed temperature sensor (RDTS) during the $\gamma $ -ray exposure of different classes of commercial multimode fibers (MMFs) acting as the sensing element. RDTS is influenced by the radiation-induced attenuation (RIA) phenomena leading to both large errors in the temperature measurements and a diminution of the useful sensing length. The amplitude of the radiation-induced temperature error strongly depends on the fiber choice and on the irradiation conditions. For the single-ended RDTS operation in the targeted Cigeo application the selection of a radiation tolerant sensing fiber will be mandatory, but not sufficient, to overcome the expected severe ambient conditions around radioactive wastes. For efficient temperature sensing up to an accumulated dose of 0.1 MGy, pre-irradiation of the selected radiation resistant (RR) fibers appears also necessary to improve the sensor performances.

In this paper, a tapered polymer fiber sensor (TPFS) is employed to detect the crack of Concrete Beam (CB). The sensing principle for crack detection is simply described based on V-number theory. The experiments are carried out by cement mixture mixed with high reactive powder to form the CB, in which the TPFSs are embedded and surface glued. Thermocouples and strain gauges are also embedded to calibrate and determine the ambient temperature and applied strain, meanwhile, the Linear Variable Differential Transformer ( LVDT) sensors are used to measure the deflection of the CBs. Four points loading test is applied for several samples to evaluate the sensors’ ability for monitoring the beam deflection and crack. Experimental results also indicate that the TPFSs can be used for post-crack detection.

Perovskite mixed valence magnetic (La0.7Ba0.3MnO3) material is explored as a magneto-optical sensor by integrating onto the surface of an optical fiber. The guiding properties of core modes excited by the material cavity are modulated by the external magnetic field. The experimental results concluded that the device exhibits linear response to applied magnetic field strength in the range of 0–20 mT with the sensitivity of 228 pm/mT and resolution of 0.87 Oe. Blue-shift phenomenon has been observed in the interference pattern, when a magnetic field is applied. Such wavelength shift is attributed to the influences of magneto-optical properties on optical-wave propagation. The results reveal the feasibility of developing an index-tuneable magneto-optical sensor using perovskite magnetic material.

An optical fiber temperature and strain fiber sensor based on the few-mode fiber (FMF) and the fiber Bragg grating (FBG) is proposed and demonstrated. The sensor unit is fabricated by a length of FMF offset splicing with one section of single-mode fiber (SMF). The temperature and strain are measured simultaneously because of the different sensitivities of the spectrum dips. The interference with the highest extinction ratio of 23 dB can be achieved. The temperature sensitivities of -34.3 pm ∕ ° C and 10.7 pm ∕ ° C and strain sensitivities of -2 pm ∕ μ e and 0.67 pm ∕ μ e are achieved, respectively. The proposed sensor may exhibit the great potential in fields of the dual-parameter measurement due to its compact structure, simple configuration.

Instead of using the fiber fusion splicer, we utilize the common fused biconical taper machine used in industry to fabricate the S tapered fiber by arc heating. We studied to measure the sensing characteristics of the S tapered fiber sensor in low concentration of solution. The results shows that the maximum sensitivity of the concentration of solution range from 2g/L(1.3336677) to 10g/L(1.3340331) is about 814.921 nm/RIU, and the resolution is 8.7247714×10-6RIU.

This study aims on the detection of PD inception voltage and tree growth in silicone rubber under DC conditions, using a fluorescent silicone fiber sensor in combination with an optical converter and the PD measuring system as well as a camera. A typical PD source was used and embedded in model samples made of transparent silicone rubber. By means of time synchronous optical and electrical measurements at positive and negative DC voltages, the results contribute to a better understanding of the degradation of silicone rubber in DC cable accessories.

We present a label-free optical fiber based sensor device to detect copper ions (Cu2+) in water. A multimode optical fiber, with its polymer cladding removed along a 1-cm length, is used for the optical sensor head, where the injected Cu2+ in the liquid phase acts as a liquid cladding for the optical mode. The various Cu2+ concentrations modulate the numerical aperture (NA) of the liquid cladding waveguide part. The degree of NA mismatch between the liquid cladding and solid cladding guided parts gives rise to an optical power transmittance change, forming the sensing principle. The presented liquid cladding fiber sensor exhibits a minimum resolvable refractive index of 2.48 &times, 10&minus, 6. For Cu2+ detection, we functionalize the sensor head surface (fiber core) using chitosan conjugated ethylenediaminetetraacetic acid (EDTA) which captures Cu2+ effectively due to the enhanced chelating effects. We obtain a limit of detection of Cu2+ of 1.62 nM (104 ppt), which is significantly lower than the tolerable level in drinking water (~30 &micro, M), and achieve a dynamic range of 1 mM. The simple structure of the sensor head and the sensing system ensures the potential capability of being miniaturized. This may allow for in-situ, highly-sensitive, heavy metal sensors in a compact format.

We review recent developments of signal processing methods for distributed fiber sensor networks, followed by detailed results about image processing for Φ-OTDR, machine learning and pulse coding for BOTDA.

International audience; This paper reports the testing results of radiation resistant fiber Bragg grating (FBG) in random air-line (RAL) fibers in comparison with FBGs in other radiation-hardened fibers. FBGs in RAL fibers were fabricated by 80 fs ultrafast laser pulse using a phase mask approach. The fiber Bragg gratings tests were carried out in the core region of a 6 MW MIT research reactor (MITR) at a steady temperature above 600°C and an average fast neutron (>1 MeV) flux >1.2 × 10$^{14}$ n/cm$^2$/s. Fifty five-day tests of FBG sensors showed less than 5 dB reduction in FBG peak strength after over 1 × 10$^{20}$ n/cm$^2$ of accumulated fast neutron dose. The radiation-induced compaction of FBG sensors produced less than 5.5 nm FBG wavelength shift toward shorter wavelength. To test temporal responses of FBG sensors, a number of reactor anomaly events were artificially created to abruptly change reactor power, temperature, and neutron flux over short periods of time. The thermal sensitivity and temporal responses of FBGs were determined at different accumulated doses of neutron flux. Results presented in this paper reveal that temperature-stable Type-II FBGs fabricated in radiation-hardened fibers can survive harsh in-pile conditions. Despite large parameter drift induced by strong nuclear radiation, further engineering and innovation on both optical fibers and fiber devices could lead to useful fiber sensors for various in-pile measurements to improve safety and efficiency of existing and next generation nuclear reactors.

An optical fiber high temperature sensor is proposed and fabricated by cascading two spherical-shape structures, which are built by a section of single mode fiber (SMF). The spherical-shape structures can realize the coupling and recoupling between the core mode and the cladding modes. Experimental results show that the sensor is capable of monitoring temperature change from 25 °C to 735 °C with sensitivity of 0.1193 nm/°C and the sensitivity of microstrain is −0.0012 nm/μe which is beneficial for encapsulation. The characteristics of the proposed sensor indicate compact, high sensitive and inexpensive properties, which can be widely applied in many fields.

MPB Communications (MPBC) is developing solutions to the monitoring requirements of spacecraft based on its fiber-laser and Fiber Bragg Grating expertise. This is cumulating in the Fiber Sensor Demonstrator for ESA’s Proba-2 that is scheduled for launch in 2007. The advantages of the MPBC approach include a central interrogation system that can be used to control a variety of different fiber-optic sensors including temperature, pressure, actuator status, and propellant leakage. This paper reviews the design and ground qualification of the FSD system in preparation for integration with Proba-2. The FSD will provide monitoring for various Proba-2 subsystems, including a hybrid propulsion system. Some of the challenges associated with using fiber-optics in space are discussed.

In this research, a temperature measurement technique was developed using fiber optic structured SMS and OTDR. Where in optical fibers singlemode-multimode-singlemode (SMS) and Optical Time Domain Reflectometer (OTDR) has been widely used for various sensors in detecting damage to the building earlier. Thereafter, calculations are performed using Borland Delphi's Lagrange Interpolation method 7. Characteristics of each of the fiber-optic fiber sensor structures that have been fabricated using multimode optical fibers with lengths of 5.5 cm, 6 cm, 6.5 cm and 7 cm and with use its operating wavelength is 1310 nm. Testing rangesuhusebesar 37oC - 67oC with every temperature rise of 10oC.Berdasarkan research results, multimode length 5.5 cm there is a graph increase with R2 of 93.7%. The increase in temperature, the loss of power generated greater. While the multimode length 6 cm, 6.5 cm, and 7 cm indicate that there is a decrease graph, for multimode length 6 cm with R2 equal to 97,7%, for multimode length 6,5 cm with R2 equal to 99,7%, for long multimode 7 cm with R2 99.2%. While based on result of calculation by Lagrange Interpolation method for suhuberstruktur SMS sensor based on result of calculation using Lagrange Interpolation method with different multimode length have same data regularity compared to temperature sensor structured SMS based on measurement result. For example, as long as 7 cm long multimode yield R2 of 99.2% for the measurement result and yield R2 of 99.3% for the calculation result.

The Fiber Sensor Demonstrator (FSD), for ESA’s Proba-2 satellite is the first demonstration of a full fiber-optic sensor network in the space environment on a satellite.

The applications of specklegram analysis techniques have been developed recently. In this paper, we represent a fiber-optic method to measure the temperature through the analysis of output specklegrams. The proposed all-fiber device excites higher-order modes through splicing a multimode fiber (MMF) to a single-mode fiber (SMF) with a core offset. The basic principle of the sensor is based on determining the change occurring to a speckle pattern when the fiber is heated under different temperature. This change in the speckle pattern is computed by comparing it with a reference speckle pattern recorded at a known temperature and therefore can be related to the temperature change. The experiments manifest the approximately linear relation between correlation coefficient and temperature. Furthermore, we also demonstrate the effects of other related parameters to the sensor.

Phase Diffraction (PD) Phase Diffraction. which is a result of the interaction of light waves with a transparent object, is exploited to characterize precisely optical properties of dielectric films coated on the optical fiber without harming any feature of the sample. Typical fiber sensor applications require films coated on the side surface of the optical fiber and optical properties of that curved films are crucial for design purposes. In this study, three Polyvinyl Alcohol (PVA) films are prepared, their thicknesses are estimated based on the phase diffraction method by fitting experimental results with a mathematical model within 2.3% error. The outcomes of this practical method show good agreement with findings of the destructive Scanning Electron Microscopy (SEM) measurements. The method has the potential to allow real time monitoring abrupt changes of surrounding medium's properties and to examine coating quality (i.e. thickness uniformity) of the film., Scientific and Technological Research Council of Turkey (TUBITAK 114E006)

In this paper, a new multipoint optical fiber system for relative humidity measurements based on Sn02-FP (Fabry-Pérot) sensing heads and an optical interrogator as single active device is presented and characterized. The interrogation of the sensing heads is carried out by monitoring the Fast Fourier Transform phase variations of the FP (Fabry-Pérot) interference frequencies. This method allows to multiplex several sensors with different wavelength spacing interference pattern. The sensors operate within a wide humidity range (20%-90% relative humidity) with low crosstalk between them. Five sensing heads have been measured using two different channels of the optical interrogator. The availability of four channels in the interrogator allows to multiplex a higher number of sensors, reducing proportionally the cost of each sensing point. The authors thank the Spanish Government projects TEC 2013-47264-C2-2-R, TEC2016-76021-C2-1-R, TEC2013- 43679-R Innocampus and the INTERREG SUDOE Project SOE3/P2/P714 as well as to the FEDER Funds.